Synthesis of the Thio‐Linked Ganglioside GM 3 epitope

The synthesis of sulfur‐linked GM 3 epitope 2 is based on acid‐catalyzed and base‐promoted S ‐glycosylation processes. As a precursor, 2‐ O ‐benzoyl‐3‐thiogalactoside 10 was required, and was obtained from 4,6‐ O ‐benzylidene‐galactoside 3 in six high‐yielding steps. Base‐promoted S ‐glycosylation of 10 with neuraminic acid functionalized β‐halogenose 11 in the presence of NaH as base and Kryptofix 21 as coactivator afforded α(2‐3)‐thio‐linked disaccharide 13 , which was readily converted to α‐halogenose 20 . Heptyl 1‐thioglycoside 22 was obtained from O ‐galactosyl trichloroacetimidate 21 and heptylthiol via acid‐catalyzed S ‐glycosylation. 22 was transformed into 2,3,6‐tri‐ O ‐acylgalactoside 26 which, via the 4‐ O ‐triflate and treatment with potassium thioacetate, followed by selective removal of the S ‐acetyl group, furnished the 2,3,6‐tri‐ O ‐acyl‐4‐thioglucoside 28 . Base‐promoted S ‐glycosylation of 28 with halogenose 20 led to fully acylated target molecule 29 , which was quantitatively converted into 2 .